Synthesis and Characterisation of Optical Sol-gel Waveguide Materials: Master's thesis

Plastics and glasses are materials traditionally used to transmit light in optical data transmission applications. Sol-gel technique takes advantage of the best parts from both materials. It is a technique, where solid organic/inorganic hybrid glass materials can be derived from a liquid phase and can have a wide variety of properties. Target for this thesis was to study sol-gel based passive optical waveguide materials for planar optical applications. Their usefulness in optics has been studied widely, but quite often these materials are not suitable due to high C-H and O-H contents. These bonds and especially O-H bonds cause strong absorption loss at telecommunication wavelength windows, which are around 1310 and 1550 nanometers. Therefore, materials were synthesised to contain these bonds as low amount as possible. Several optical waveguide materials were synthesised within the framework of this thesis. Two of them were optically characterised (refractive indices, birefringences and optical losses) to study their applicability for planar optical applications. Raman technique was employed to study reaction kinetics in one system. In addition, a fluorinated silane precursor was synthesised and characterised by nuclear magnetic resonance (NMR). Fluorination (C-H to C-F) decreases optical losses in sol-gel waveguide materials. Other ways to decrease optical losses are deuteration (C-H to C-D) and chlorination (C-H to C-Cl). Best results were achieved with chlorinated materials. Surface roughness of the planar waveguide structure (slab structure) was 3 nanometers. Optical losses of the waveguide were around 1 dB/cm at 1310 and 1550 nm wavelengths and around 0.4 dB/cm at 830 nm wavelengths. Film thickness for the same material was approximately 4 micrometers.